[Physics] Clock time vs. common sense time

[Ilja Schmelzer]

2016-10-26 12:00 GMT+02:00, physics-request at tuks.nl <physics-request at tuks.nl>:
> But this is very telling - because the earth rotational clock (or any
> rotating frame of reference, such as a spinning disk rotating past a light)
> can be constructed as a clock such that it obeys exactly your definition of
> "a working clock."

Any time-like coordinate would do it.

Or, in other words, to be a "working clock" in the usual meaning of
measuring common sense time, the clock would have to measure some
time-like coordinate.  This is a necessary condition.

Unfortunately, it is not sufficient.  There are many imaginable
time-like coordinates, but there is only one time.  And GR does not
have any idea what could distinguish true time from all the other
time-like coordinates.   So it choses the positivist variant of "we
have no way to identify true time", which is "true (absolute) time
does not exist".

> But this statement renders "time" to be effectively meaningless, it is "a
> number on a clock" ; this is not what Einstein actually meant - the clock
> readings have "meaning" in the theory of relativity - because they refer to
> the speed of real processes in nature.

And I do not say it is meaningless.  It, indeed, defines a lot of
interesting things.  In particular how we age ourselves. Because the
processes in our body are also some sort of clock - even if only a
very inaccurate one.

> So we can't render the clock
> readings as meaningless - in fact because the theory does attribute
> physical meaning in this way, it is inherently testable. You can't just say
> "what can't be measured doesn't exist."

Nobody says the clock readings are meaningless.  I say that they don't measure
common sense time.  They measure clock time.  Which is something important,
and, in particular, a good approximation in everyday life for common sense time,
but which is nonetheless something different.

What I say is that GR has no way to distinguish true time from any of
the many other imaginable time-like coordinates. And that it makes,
therefore, testable predictions only about clock time, not about true
time.

> If relativity is a true scientific
> theory, then all of its assumptions have to be testable (Popper)

More accurate, please.  A scientific theory should be able to make
testable predictions.  More testable predictions means higher value of
that scientific theory.

But there is no claim at all that all statements, or all assumptions
of a scientific theory have to be testable.

> we have no other
> choice but to conclude that when an atomic clock says it is in the future,
> it is actually in the present - this should be a big problem for the theory
> of relativity,

Sorry, but this makes no sense. No clock says, never, that it is in
some future.  Everything is always in the present.  If you have two
clocks, and they show different times, you usually have no way to say
which of them is correct.  And even if you have, the wrong clock is
not "telling it is in the future",  but simply makes a different
(wrong) claim about the time now.  And it is certainly not a problem
for a theory, if it predicts that, say, some clocks go slower under
some special circumstances, like extreme temperature or pressure or
whatever.